1. Field of the Invention
The present invention relates generally to medical diagnosis of disease states from tissue samples and, more specifically, to a device and method for separating fragments of tissue biopsy samples from a fixative and capturing them for processing.
2. Description of Related Art
Many of us have noticed a strange-looking mole or felt a lump. "Is it cancer?" is often the first thought that comes to mind. Often a physician will take a look and tell us that there is nothing to worry about. At other times, the physician will have to take a biopsy or tissue sample from the patient at the physician's office, out patient department, or hospital. The tissue sample is then sent to a special pathology laboratory of a hospital or to a private pathology practice for diagnosis.
There the tissue is usually studied by a pathologist, a physician who is specially trained to recognize and interpret histological and cytological abnormalities. The pathologist can diagnose many disease states, as well as cancer. The pathologist provides a detailed written evaluation of tissue samples as an integral part of modern medicine. After the pathologist examines the sample and renders a gross description, the histology department processes and prepares sections of the sample, which are placed on slides for microscopic observation. Unfortunately, it is not always easy to properly prepare a tissue sample for proper evaluation. The suspicious tissue or growth may be tiny and located in an inaccessible area. Therefore, the tissues samples, which may be surgically cut, curetted, or scraped from the patient, many times consist of small fragments. These small samples are precious, since it may not be possible to procure a second sample, and since only one of many fragments may contain specific abnormal findings which allow the diagnosis to be made.
Furthermore, the process of preparing the tissue for microscopic examination is time-consuming and may result in losing or damaging the tissue sample. The samples are often obtained from a patient, measured and described by the pathologist, and placed directly in the fixative, usually 10% formalin. The fixation process preserves cellular detail, stabilizes the tissue, and makes the sample amenable to the later steps of processing. The tissue samples can be conveniently stored in the formalin fixative until processing is started by the histology department.
Preparation of microscope slides entails embedding the tissue in a hard matrix and preparing sections of the embedded tissue. Briefly, the process comprises removing the tissue samples from the fixative and dehydrating them by passing them through a graded series of mixtures of alcohols, xylene and paraffin. A dehydrated sample is first treated with xylene which is miscible both with alcohol and paraffin, allowing the alcohol to be replaced with xylene, and the xylene to be then replaced with paraffin. Thus, the tissue samples are infiltrated with a paraffin wax matrix material that will support the tissue when sections, usually 3-5 .mu.m in thickness, are cut.
Considerable progress has been made in automating tissue processing for a busy histology laboratory. Various instruments are used to automatically dehydrate the samples and infiltrate them with paraffin. These instruments may be quite large and complex because they must contain a heated chamber to keep the paraffin molten. The first step is for the pathologist or a special assistant to remove the samples from the fixative and transfer them to a special processing cassette 10 (see FIG. 1). The processing cassette 10 comprises a base unit 12 and a lid 14. The lid 14 is removable so that samples can be easily placed into the cassette 10 (see FIG. 2). Both the base 12 and the lid 14 are perforated so that processing solutions may easily percolate through the cassette. Because formalin is toxic and allergenic, protective gloves are worn when the samples are transferred. One can easily crush or distort a particulate or fragile tissue sample. Unfortunately, the use of forceps may also crush the samples.
Once the tissue samples are in the cassette 10, they are automatically moved through the various solutions necessary to dehydrate and embed the tissue. The entire process usually takes between 4-12 hours. At the conclusion of the processing the paraffin-infiltrated samples are removed from the cassette 10 and cast into a block of paraffin for sectioning with a special microtome. The sections are placed on a glass microscope slide, xylene is used to remove the paraffin, and the sections are rehydrated and stained with special dyes to reveal cellular details. A thin glass coverslip is often placed over the stained sections, and the pathologist then microscopically examines the sections and arrives at a diagnosis.
Although the automatic processing instruments save considerable time and effort, they also introduce a number of problems. As already explained, the samples are often tiny and irreplaceable. Even if one laboriously removes all the tissue samples from the fixative and places them in the cassette, it is likely that some of the precious tissue biopsy samples will pass through the cassette perforations, or even through a space between the cassette base 12 and lid 14, and be lost during the infiltration process. In addition, pieces of tissue (called "floaters") may escape from one cassette and enter and mix with the samples in another cassette, thereby resulting in false diagnoses.
Workers have attempted to strain the tissue samples from the fixative, but the smallest samples often become stuck to the wire strainer and are damaged during removal. Likewise, attempts have been made to use filter material such as filter paper to capture the fragments, but removal of the samples from loose paper is cumbersome at best. The dilemma remains: the one tissue fragment that is lost during processing may be the sole sample that allows a proper diagnosis. Thus, the apparently simple problem of separating tissue samples from fixative may actually become a life-and-death matter.